Ingan-based light-emitting diode chip and a method for the production thereof

ABSTRACT

A light-emitting diode chip ( 1 ), in which over a substrate ( 2 ), a series of epitaxial layers ( 3 ) with a radiation-emitting active structure ( 4 ) based on InGaN is disposed. Between the substrate ( 2 ) and the active structure ( 4 ), a buffer layer ( 20 ) is provided. The material or materials of the buffer layer ( 20 ) are selected such that their epitaxial surface ( 6 ) for the epitaxy of the active structure ( 4 ) is unstressed or slightly stressed at their epitaxial temperature. The active structure ( 4 ) has In-rich zones ( 5 ), disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in other regions of the active structure ( 4 ). A preferred method for producing the chip is disclosed.

[0001] The invention relates to an InGaN-based light-emitting diode chip and to a method for producing an InGaN-based light-emitting diode chip.

[0002] The term InGaN-based light-emitting diode chips in conjunction with the present invention is understood fundamentally to mean all light-emitting diode chips whose radiation-emitting zone has InGaN or related nitrides as well as mixed crystals based thereon, such as Ga(Al,In)N.

[0003] InGaN-based light-emitting diode chips are known for instance from The Blue Laser Diode by Shuji Nakamura and Gerhard Fasol, Springer Verlag Berlin Heidelberg 1997, page 209 ff.

[0004] The object of the invention is to make a light-emitting diode chip of the type defined at the outset available that has the highest possible radiation intensity. Moreover, a method for producing such a light-emitting diode chip is to be disclosed.

[0005] The first of these objects is attained with a light-emitting diode chip having the characteristics of claim 1. Advantageous refinements are the subject of claims 2-4. The other object is attained by a method defined by claim 5. Preferred refinements of this method are the subject of claims 6-8.

[0006] In a light-emitting diode chip of the invention, a series of epitaxial layers with a radiation-emitting active structure based on InGaN is grown on a substrate. Between the substrate and the radiation-emitting active structure is a buffer layer, comprising one or more layers. The material or materials of the buffer layer are selected such that their epitaxial surface for the epitaxy of the radiation-emitting active structure is unstressed or slightly stressed at their epitaxial temperatures. The radiation-emitting active structure has zones richer in In disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in other regions of the active structure.

[0007] In a preferred refinement of the light-emitting diode chip, the substrate substantially comprises electrically conductive SiC. As a result, the chip can advantageously be realized with a typical light-emitting diode chip structure, in which the contact faces are disposed on opposed sides of the chip. Consequently, current impression over a large region of the lateral chip cross section is possible in a simple way. In contrast to this, in chips with an electrically insulating substrate, the side toward the substrate of the series of epitaxial layers must be contacted from their surface. This involves markedly greater production complexity and expense, because the series of epitaxial layers, after being produced, have to be provided with etched trenches or grown in structured fashion in order to be able to contact the n-side of the active structure.

[0008] In an especially preferred refinement of the light-emitting diode chip, the active structure has a multiple- quantum-well structure, in which at least one quantum well contains the In-rich zones.

[0009] Especially preferably, the series of buffer layers has an AlGaN:Si that is a few hundred nanometers thick and is followed in the growth direction by a GaN:Si layer. The latter has a thickness between 1 μm and 3 μm. The surface of the GaN:Si layer forms the epitaxial surface for the epitaxy of the radiation-emitting epitaxial layer series and at the epitaxial temperature or epitaxial temperatures of the InGaN-based layer, it is unstressed or slightly stressed.

[0010] In the method of the invention, a radiation-emitting epitaxial layer series with a radiation-emitting active structure based on InGaN is deposited over a substrate. Before the epitaxy of the radiation-emitting active structure, a buffer layer or a series of buffer layers is grown on the substrate, the epitaxial surface of which layer or series, for the growth of the radiation-emitting active structure, is unstressed or slightly stressed at the epitaxial temperature or temperatures thereof.

[0011] With this method, it is advantageously achieved that the active structure has In-richer zones disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in other regions of the active structure.

[0012] In an especially preferred embodiment of the method, as the active structure, a single-quantum-well structure or a multiple-quantum-well structure with InGaN quantum wells is created, and an SiC-based substrate is used.

[0013] As the buffer layer, preferably over the substrate first an AlGaN:Si layer a few hundred nanometers thick is deposited epitaxially, over which a GaN:Si layer is grown epitaxially. The thickness of the GaN:layer is between 1 μm and 3 μm, and over its surface, the radiation-emitting epitaxial layer series is deposited.

[0014] As the epitaxy method, metal-organic vapor phase epitaxy (MOVPE) is preferably suitable.

[0015] Other advantageous features and refinements of the invention will become apparent from the exemplary embodiments described below in conjunction with FIGS. 1a-2. Shown are:

[0016]FIG. 1a, a schematic illustration of a section through a first exemplary embodiment;

[0017]FIG. 1b, a schematic illustration of an advantageous contact design and of an advantageous way of mounting the first exemplary embodiment;

[0018]FIG. 2, a schematic illustration of a section through a second exemplary embodiment, including its advantageous type of mounting.

[0019] In the drawings of the various exemplary embodiments, components that are the same or function the same are each identified by the same reference numerals.

[0020] In the light-emitting diode chip 1 of FIG. 1a, a radiation-emitting active structure 4 is disposed over an SiC substrate 2. In the present example, this active structure has an InGaN single quantum well 7.

[0021] The radiation-emitting active structure 4 includes a plurality of In-rich zones 5, disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in the other regions of the active structure 4. The In content in the In-rich zones 5 is for instance up to 40%.

[0022] Over the radiation-emitting active structure 4, a thin p-conductively doped AlGaN epitaxial layer 8 and a p-conductively doped GaN layer 9 that is for instance 200 nm thick are grown.

[0023] It is equally possible for instance to provide an InGaN-based radiation-emitting active structure 4 with a double-hetero structure or a multiple-quantum-well structure (MQW) structure with a plurality of quantum wells.

[0024] The SiC substrate 2 is electrically conductive and is at least partly permeable to the radiation emitted by the epitaxial layer series 3.

[0025] Between the substrate 2 and the active structure 4 is a buffer layer 20, which contains an AlGaN:Si layer 10 a few hundred nanometers thick, which is followed in the growth direction by a GaN:Si layer 11. The GaN:Si layer 11 has a thickness between 1 μm and 3 μm, and its surface facing away from the substrate 2, in the production of the chip 1, forms the epitaxial surface 6 for the epitaxy of the InGaN-based radiation-emitting active structure 4.

[0026] In the contact design and type of mounting of the chip of FIG. 1b, which with respect to its epitaxial layer structure 3 is equivalent to the chip 1 of FIG. 1a, a bondable p-contact layer 12 is applied to the p-conductively doped GaN layer 9. This contact layer comprises Ag, or a PtAg and/or PdAg alloy, or is composed for instance of a first layer that is permeable to radiation and a reflective second layer. In the second alternative, the first layer essentially comprises Pt and/or Pd, for instance, and the second layer substantially comprises Ag, Au, and/or Al, or a dielectric mirror layer, for instance.

[0027] On its side 15 facing away from the epitaxial layer series 3, the SiC substrate 2 is provided with a contact metallization 13, which covers only part of this primary face 15 and is embodied as a bond pad for wire bonding.

[0028] The chip 1 is mounted by means of die bonding with its p-side, that is, the p-contact layer 12, on a chip mounting face 19 of an electric leadframe 14. The n-contact metallization 13 is connected via a bond wire 17 to a connection part 18 of the leadframe 14.

[0029] The light output from the chip 1 is effected via the free region of the primary face 15 of the SiC substrate 2 and via the chip edges 16.

[0030] Optionally, the chip 1 has an SiC substrate 2 that is thinned after the epitaxy of the epitaxial layer series 3. It is equally possible for the substrate 2, after the epitaxy of the epitaxial layer series 3, to be removed completely from this layer or series, creating a so-called thin-film LED.

[0031] It is understood that the chip 1 of the invention can also be mounted with its substrate side, that is, so-called “up side up” mounting, on the chip mounting face 13 of an electrical leadframe 14. The contact design should then naturally be adapted to that type of mounting. Possible materials for suitable contact metallization are known from the prior art and will therefore not be described further at this point.

[0032] The exemplary embodiment shown in FIG. 2 differs from that of FIGS. 1a and 2 b essentially in that the chip edges 16 in the region below the active structure 4 are oblique to the primary direction in which the quantum well 7 extends; in the further course toward the underside, they then change over to side faces that are perpendicular again to the primary direction in which the quantum well 7 extends, so that on the one hand improved output of the radiation generated in the active zone through the side faces is attained, and on the other, reliable flip-chip mounting with conventional chip mounting systems is possible. The angle α of the regions of the side faces that are oblique to the quantum well is preferably between 20° and 80°, and an angle of approximately 30° is especially advantageous.

[0033] This chip structure of FIG. 2 is created by means of a shaping saw blade, whose end face is V-shaped and with which the epitaxy wafer, before the separation into individual chips 1, is sawn into the shape shown in FIG. 2.

[0034] In a method for producing a light-emitting component of the exemplary embodiments, first by means of metal organic gas phase epitaxy (MOVPE), the AlGaN:Si layer 10 a few hundred nanometers thick and the GaN:Si layer 11 are applied to the substrate 2. Next, the radiation-emitting active structure 4 is deposited, in which the epitaxial surface intended for it, which in the present case is formed by the free primary face of the GaN:Si layer 11, is unstressed or slightly stressed at the epitaxial temperature or temperatures of the InGaN-based structure.

[0035] Below, a comparison test of two chips 1 produced identically except for the epitaxial surface of the GaN:Si layer 11 by the method described above will be explained.

[0036] Sample 1 is a chip in which the epitaxial surface 6 is severely compressively stressed at the epitaxial temperature of the InGaN-based layer.

[0037] Conversely, in sample 2, the epitaxial surface 6 has no tension or only slight tension at the epitaxial temperature of the InGaN-based layer.

[0038] An analysis of the chips shows that the sample 1 has very smooth boundary faces between the various epitaxial layers of the series of active layers and has a homogeneous In content of approximately 15%. Conversely in sample 2, the boundary faces between the various epitaxial layers of the active layer series are very rough, and the structure has dotlike locally raised lattice constants, which correspond with locally increased In contents of up to 40%.

[0039] When mounted in a 5-mm radial structural form with a 20 mA forward current, sample 2 has a markedly increased performance over sample 1, with a simultaneous shift in the peak wavelength toward greater wavelengths.

[0040] It is understood that the explanation of the invention in terms of the above exemplary embodiments is not to be understood as a limitation to these embodiments. On the contrary, the invention can be used in particular in all light-emitting diode chips in which the active zone is based on InGaN. 

1. A light-emitting diode chip (1), in which a series of epitaxial layers (3) with a radiation-emitting, InGaN-based active structure (4) is disposed over a substrate (2), and a buffer layer or series of buffer layers (20) are disposed between the substrate (2) and the active structure (4), and the material or materials of the buffer layer or series of buffer layers (20) are selected such that for the epitaxy of the active structure (4) their epitaxial surface (6) is unstressed or slightly stressed at their epitaxial temperature, and the active structure (4) has In-rich zones (5) disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in other regions of the active structure (4).
 2. The light-emitting diode chip (1) of claim 1, in which the substrate (2) substantially comprises SiC.
 3. The light-emitting diode chip (1) of claim 1 or 2, in which the active structure (4) has a single-quantum-well structure or a multiple-quantum-well structure, in which the quantum well, or the at least one quantum well, contains the In-rich zones (4).
 4. The light-emitting diode chip (1) of one of claims 1-3, in which the series of buffer layers (20) has an AlGaN:Si layer (9) downstream of which in the growth direction is a GaN:Si layer (10), which has a thickness between 1 μm and 3 μm and whose surface forms the epitaxial surface (6) for the epitaxy of the radiation-emitting series of epitaxial layers.
 5. A method for producing an InGaN-based light-emitting component, in which a series of epitaxial layers (3) with a radiation-emitting InGaN-based active structure (4) is deposited on a substrate (2), and before the epitaxy of the radiation-emitting active structure (4) a buffer layer or series of buffer layers (20) is grown on the substrate (2), whose epitaxial surface for the epitaxy of the radiation-emitting active structure (4) is unstressed or slightly stressed at their epitaxial temperatures.
 6. The method of claim 5, in which a multiple-quantum-well structure with an InGaN quantum well is created as the active structure (4).
 7. The method of claim 5 or 6, in which as the substrate (2), an SiC substrate is used.
 8. The method of one of claims 5-7, in which over the substrate (2), first an AlGaN:Si layer is deposited a few hundred nanometers thick, over which a GaN:Si layer is grown that has a thickness between 1 μm and 3 μm, and on the surface of which the radiation-emitting active structure (4) is deposited.
 9. The method of claim 6, in which over the substrate (2), first an AlGaN:Si layer (10) is deposited a few hundred nanometers thick, over which a GaN:Si layer (11) is grown that has a thickness between 1 μm and 3 μm, and on a surface of which the radiation-emitting active structure (4) is deposited.
 10. The method of claim 7, in which over the substrate (2), first an AlGaN:Si layer (10) is deposited a few hundred nanometers thick, over which a GaN:Si layer (11) is grown that has a thickness between 1 μm and 3 μm, and on a surface of which the radiation-emitting active structure (4) is deposited.
 11. The light-emitting diode chip (1) of claim 2, in which the series of buffer layers (20) has an AlGaN:Si layer (10) downstream of which in the growth direction is a GaN:Si layer (11), which has a thickness between 1 μm and 3 μm and whose surface forms the epitaxial surface (6) for the epitaxy of the radiation-emitting series of epitaxial layers.
 12. The light-emitting diode chip (1) of claim 3, in which the series of buffer layers (20) has an AlGaN:Si layer (10) downstream of which in the growth direction is a GaN:Si layer (11), which has a thickness between 1 μm and 3 μm and whose surface forms the epitaxial surface (6) for the epitaxy of the radiation-emitting series of epitaxial layers.
 13. The light-emitting diode chip (1) of claim 2, in which the active structure (4) has a single-quantum-well structure or a multiple-quantum-well structure, in which the quantum well, or the at least one quantum well, contains the In-rich zones (5).
 14. The method of claim 6, in which as the substrate (2), an SiC substrate is used. 